UK Rivers Research Articles

Quantifying impacts of titanium dioxide nanoparticles on natural assemblages of riverine phytobenthos and phytoplankton in an outdoor setting

Impacts of widespread release of engineered titanium dioxide nanoparticles (nTiO2) on freshwater phytoplankton and phytobenthic assemblages in the field, represents a significant knowledge gap. Using outdoor experiments, we quantified impacts of nTiO2 on phytoplankton and periphyton from UK rivers, applied at levels representative of environmentally realistic concentrations (0.05 mg/L) and hot spots of accumulation (5.0 mg/L). Addition of nTiO2 to river water led to rapid temporal size changes in homoagglomerates and many heteroaggregates of nTiO2 with cells in the phytoplankton, including green algae, pennate and centric diatoms, increasing settlement of some cells. Changes in phytoplankton composition were evident after 72-h resulting from a significant decline in the relative abundance of very small phytoplankton cells (1–3 μm), often accompanied by increases in centric diatoms at both concentrations. Significant changes detected in the composition of the phytobenthos after 12 days, following nTiO2 treatments, were not evident when using benthic diatoms alone after 56 days. A lack of inhibition in the maximum quantum yield (Fv/Fm) in phytobenthos after 72-h exposures contrasted with a significant inhibition in Fv/Fm in 75% of phytoplankton samples, the highest recorded in Rutile nTiO2 exposures at both concentrations of nTiO2. After 12 days, strong positive stimulatory responses were recorded in the maximum relative electron transport rate (rETRmax) and the maximum non-photochemical coefficient (NPQmax), in phytoplankton and phytobenthos samples exposed to the higher Anatase nTiO2 concentration, were not measured in Rutile exposed biota. Collectively, these results indicate that the Rutile phase of nTiO2 has more negative impacts on freshwater algae than the Anatase form, at specific time scales, and phytoplankton may be more impacted by nTiO2 than phytobenthos. We caution that repeated release of nTiO2, could lead to significant changes in riverine algal biomass and species composition, dependent on the phase and concentration of nTiO2.

Hydrological properties predict the composition of microbial communities cycling methane and nitrogen in rivers

Sediment microbial communities drive the biogeochemical cycles that make rivers globally important sources and sinks of carbon (C) and nitrogen (N). The structure of these communities is strongly determined by the local physico-chemical environment. However, we currently lack an understanding of the factors that determine microbial community structures at the catchment scale. Here, we show that the contribution of groundwater to total river flow (quantified as base flow index; BFI) predicts the structure and diversity of the different microbial functional groups that cycle N and C across nine UK rivers, spanning a geological BFI gradient from 0.23 (clay sediment) to 0.95 (chalk gravel sediment). Furthermore, the GC-content (percentage of guanine-cytosine bases in a DNA sequence) and codon-usage bias of ammonia monooxygenase DNA sequences, and the hydrophobicity and net-charge of the corresponding amino acid sequences, were all strongly correlated with BFI, likely reflecting physiological adaptations to different riverbed sediment structure along the BFI gradient. Our results offer an opportunity to overcome the “paradox of scales” that has seen microbial ecologists focus on small- rather than large-scale environmental variables, enabling us to scale-up our understanding of microbial biogeochemistry to the catchment and beyond.

Pandemic plus? The antibiotic resistance lurking in our rivers

The battle against antimicrobial resistance is intensifying and there may be another frontier: our water supply. In this episode of The PJ Pod, Carolyn Wickware, investigations editor, looks at the emerging evidence that UK rivers are becoming a dangerous ‘breeding ground’ for bacteria resistant to antibiotics that could adversely affect human health. Alistair Boxall, professor […]

Discharge of bacteria from sewage into UK rivers risks antimicrobial resistance, experts warn

Discharge of bacteria from sewage into UK rivers risks antimicrobial resistance, experts warn

Use of Abstraction and Discharge Data to Improve the Performance of a National‐Scale Hydrological Model

AbstractAcross the UK, water abstracted from ground, surface, and tidal stores is regulated through a system of licenses to protect both the sources and the environment. Similar permits are required for discharging wastewater to rivers or onto the ground. These abstractions and discharges can have a significant impact on UK Rivers, but measurements are not readily available, which discourages their use in hydrological models of river flows. However, these very unique data sets provide a means to improve the performance of spatially distributed hydrological models, particularly during periods when abstraction regulations change and at ungauged river locations. To demonstrate this, point source abstraction and discharge measurements across England have been transformed into 1 × 1 km resolution gridded data and used with an enhanced formulation of the Grid‐to‐Grid (G2G) hydrological model where these processes are mathematically represented. A comparison of G2G‐simulated and gauged river flows for 605 catchments across England between 1999 and 2014 indicates that model simulation of river flows is generally improved at gauged locations downstream of abstraction/discharge sites. The main improvement is in the simulation of low flows, for which the median performance is improved by 10.7%, however, the impact on simulation of high river flows is more modest (1.5% improvement). These results demonstrate the potential gains available to the international hydrological and land‐surface modeling community from using records of actual water use (where available) in models, in place of more widely used national statistics.

Evaluating the performance of taxonomic and trait-based biomonitoring approaches for fine sediment in the UK

Fine sediment is a leading cause for the decline of aquatic biodiversity globally. There is an urgent need for targeted monitoring to identify where management methods are required in order to reduce the delivery of fine sediment to aquatic environments. Existing sediment-specific biomonitoring indices and indices for general ecological health (taxonomic and trait-based) developed for use in the UK were tested in a representative set of lowland rivers in England that consisted of a gradient of fine sediment pressures (deposited and suspended, organic and inorganic). Index performance was modelled against environmental variables collected during sampling and hydrological and antecedent flow variables calculated from daily flow data. Sediment-specific indices were indicative of surface sediment deposits, whereas indices for general ecological health were more closely associated with the organic content of fine sediment. The performance of biotic indices along fine sediment gradients was predominantly dependent on hydrological variability. Functional diversity indices were poorly related to different measures of fine sediment, and further development of traits-based indices and trait databases are recommended. In summary, the results suggest that sediment-specific biomonitoring tools are suitable for evaluating fine sediment stress in UK rivers when index scores are viewed within the context of local hydrology.

Authors\u2019 response on Perkins et al. (2021) \u201cDead in the water: comment on \u201cDevelopment of an aquatic exposure assessment model for imidacloprid in sewage treatment plant discharges arising from use of veterinary medicinal products\u201d

In 2020, Anthe et al. published a newly developed model to predict imidacloprid surface water concentrations stemming from sewage treatment plant (STP) effluent as a consequence of the use of veterinary medicinal products containing imidacloprid in the UK (Anthe in Environ Sci Eur (2020) 32:147, https://doi.org/10.1186/s12302-020–00424-4). The modelled data indicate that these veterinary medicinal products make only a very small contribution to the levels of Imidacloprid observed in the UK water monitoring programme.The commentary by Perkins et al. (Perkins in Environ Sci Eur (2021) 33:88, https://doi.org/10.1186/s12302-021-00533-8) questioned the validity and conclusions of the modelling approach. We believe the modelling approach, which considered what we anticipated to be, the major exposure pathways, gives a realistic picture of the chronic emission via STPs to UK rivers.

Geosocialities, Flow and Renewal in Microbial Rivers

This article draws on interview data and insights from environmental studies and somatic therapy to argue for the significance of thinking ‘with rivers’ in order to reaffirm human and nonhuman entanglements in the current challenges presented by anthropogenic devastation. River microbial communities are unintelligible and complex entities due to their unclear origin and continuous flow downstream. The account of one environmental scientist is presented to consider how the metaphors of movement used in the riverine context assist in exploring the complicated dynamics of fluid communities facing constantly changing environments I call ‘microbial rivers’. A pollution incident affecting a UK river, where microbial communities responded by growing in number and activity, further illustrates the intersection of communities and ecosystems in their adaptation to troubling human interventions. Engaging with somatic understandings of trauma, this article proposes thinking with flow as a possibility to reimagine the capacity for renewal when experiencing debilitating adversities, thus countering apocalyptic responses of immobility in the face of environmental destruction and inviting novel opportunities for growth for human and nonhuman communities.

Anthropogenic sediment traps and network dislocation in a lowland UK river

AbstractFarm ponds, reservoirs and in‐stream weirs exist in most lowland UK river catchments and often dominate natural features such as lakes, wetlands, floodplains and debris dams. Artificial structures have served multiple purposes, including provision of power for historic flour milling and iron ore crushing and provision of water for medieval fishponds, canals, crop irrigation and potable supply. Although unintentional, they can significantly affect longitudinal connectivity, including sediment delivery pathways, through river catchments.We report results from three spatially nested case studies that were undertaken in the Rother catchment, ranging in scale from small farm ponds of a few square metres in area, to larger in‐stream weirs and reservoirs (locally called ponds). Reservoirs typically trap sediment, decreasing sediment availability downstream, while inducing valley sediment accumulation upstream. We focus on the quantity and particle size characteristics of sediment trapped behind these structures compared to catchment soils and to sediments that are transported through, and deposited in, ‘natural’ gravel‐bed reaches.At all scales our results demonstrate that sediment trapping and release are particle size specific. Fine to coarse sands (125 μm to 2 mm diameter) and coarser sediments are retained behind structures at all scales, while silts and clays (<63 μm diameter) and organic matter are generally depleted in the stored sediment. Even though 75% of the surveyed reservoirs have very low estimated trap efficiencies (<5%), they slowly fill over time with sediment.An important management question relates to the likely benefits of impoundment, structure or sediment removal, and whether fine (here defined as <63 μm) or coarser (>63 μm) sediment is a priority for management.

Successful modelling of river dissolved oxygen dynamics requires knowledge of stream channel environments

Water quality in lowland rivers is sensitive to changes in flow during summer dry periods, when high temperatures and low pollutant dilution are problematic and may reduce oxygen concentrations to levels of ecological concern. A 10-year period of monitoring data was collated for a typical small lowland UK river. Two hourly-resolution applications of a process-based water quality model (QUESTOR) were made, with and without local knowledge, to establish whether specific information on stream channel hydraulics is an essential precursor to successful simulation. Results showed this information to be necessary, with considerably better goodness-of-fit statistics obtained when the local knowledge was used. In this regard, mean improvements in Nash-Sutcliffe Efficiency across all monitoring sites were from −0.33 to 0.18 and from 0.24 to 0.78 for dissolved oxygen and water temperature respectively. Percent bias was within 10% for the local model. The 10-year record also allowed a detailed characterisation of how changes in flow, as described by a comprehensive range of Indicators of Hydrological Alteration, relate to the water quality determinants. Analysis revealed these dynamics were also captured more realistically when the model was driven by local knowledge. The research concludes that river dissolved oxygen simulations driven by national-level information are of some value as screening tools, but model refinement supported by sufficient provision of local information is necessary when detailed simulations are required to support specific decision-making.

Assessing the feasibility and value of employing an ecosystem services approach in chemical environmental risk assessment under the Water Framework Directive

The feasibility and added value of an ecosystem services approach in retrospective environmental risk assessment were evaluated using a site-specific case study in a lowland UK river. The studied water body failed to achieve good ecological status temporarily in 2018, due in part to the exceedance of the environmental quality standard (annual average EQS) for zinc. Potential ecosystem service delivery was quantified for locally prioritised ecosystem services: regulation of chemical condition; maintaining nursery populations and habitats; recreational fishing; nature watching. Quantification was based on observed and expected taxa or functional groups within WFD biological quality elements, including macrophytes, benthic macroinvertebrates and fish, and on published functional trait data for constituent taxa. Benthic macroinvertebrate taxa were identified and enumerated before, during and after zinc EQS exceedance, enabling a generic retrospective risk assessment for this biological quality element, which was found to have good ecosystem service potential. An additional targeted risk assessment for zinc was based on laboratory-based species sensitivity distributions normalised using biotic-ligand modelling to account for site-specific, bioavailability-corrected zinc exposure. Risk to ecosystem services for diatoms (microalgae) was found to be high, while risks for benthic macroinvertebrates and fish were found to be low. The status of potential ecosystem service delivery (ESD) by fish was equivalent to high ecological status defined under the WFD, while ESD was higher for benthic macroinvertebrates than defined by WFD methods. The illustrated ecosystem services approach uses readily available data and adds significantly to the taxonomic approach currently used under the WFD by using functional traits to evaluate services that are prioritised as being important in water bodies. The main shortcomings of the illustrated approach were lack of: representation of bacteria and fungi; WFD predicted species lists for diatoms and macrophytes; site-specific functional trait data required for defining actual (rather than potential) ecosystem service delivery.

Acute riverine microplastic contamination due to avoidable releases of untreated wastewater

Wastewater discharge to rivers is a controversial practice that compromises water quality, aquatic habitats and human health worldwide. Here we show how untreated wastewater laced with microplastics and raw sewage is routinely discharged into UK river flows that are too low to disperse the microplastics downstream. These ‘dry weather’ spills lead to acute microplastic contamination of river bed habitats. Many aquatic fauna feed in the benthic zone, the quality of which affects the entire riverine ecosystem. All microplastic types accumulate to high concentrations on the channel bed until flushed downstream by floods. These findings pose fundamental questions about the sustainable management of urban wastewater. Treating the wastewater would shut down the major source of microplastic fragments and microbeads in such rivers and prevent their transport to the ocean. Riverine microplastic transport is primarily partitioned between: (1) continuous transport at low concentrations of synthetic fibres from treated wastewater effluent; and (2) episodic flood-driven transport of the full microplastic assemblage entrained from contaminated channel beds. Focusing only on the buoyant non-flood microplastic load can produce highly unrepresentative assessments of riverine microplastic contamination. Climate warming and urban population growth will intensify the microplastic burden on many river ecosystems as summer baseflows decline and wastewater fluxes increase.

The fractionation of phosphorus in UK chalk stream surface waters and its relevance to the regulation and management of water quality

The regulatory management of river water quality requires measurements of phosphorus that are operationally viable and meaningful in terms of insight into its effects. This need is a particular concern in globally rare and ecologically sensitive chalk streams. P data pertaining to rivers are commonly limited to soluble reactive P; other fractions of P may be of concern but are not routinely monitored. This study seeks to establish the nature and extent of non-regulated forms of P in UK chalk streams. Whilst soluble reactive P in two southern English chalk streams was found to comprise the majority of reactive P in surface waters in the majority of samples, 15–20% of the total reactive P was within other size fractions greater than 0.22 μm. The contribution of reactive P to the total P was highly variable. We conclude that, with some adjustments, the established method of regulatory monitoring of P in UK rivers is viable and valuable. In cases where the levels of reactive P are not consistent with ecological status and/or expected outcomes of programmes of measures, we recommend that targeted analysis of non-regulated forms of P is undertaken as a means to guide and focus management interventions.

Signal crayfish burrowing, bank retreat and sediment supply to rivers: A biophysical sediment budget

AbstractBurrowing into riverbanks by animals transfers sediment directly into river channels and has been hypothesised to accelerate bank erosion and promote mass failure. A field monitoring study on two UK rivers invaded by signal crayfish (Pacifastacus leniusculus) assessed the impact of burrowing on bank erosion processes. Erosion pins were installed in 17 riverbanks across a gradient of crayfish burrow densities and monitored for 22 months. Bank retreat increased significantly with crayfish burrow density. At the bank scale (<6 m river length), high crayfish burrow densities were associated with accelerated bank retreat of up to 253% and more than a doubling of the area of bank collapse compared with banks without burrows. Direct sediment supply by burrowing activity contributed 0.2% and 0.6% of total sediment at the reach (1.1 km) and local bank (<6 m) scales. However, accelerated bank retreat caused by burrows contributed 12.2% and 29.8% of the total sediment supply at the reach and bank scales. Together, burrowing and the associated acceleration of retreat and collapse supplied an additional 25.4 t km−1 a−1 of floodplain sediments at one site, demonstrating the substantial impact that signal crayfish can have on fine sediment supply. For the first time, an empirical relation linking animal burrow characteristics to riverbank retreat is presented. The study adds to a small number of sediment budget studies that compare sediment fluxes driven by biotic and abiotic energy but is unique in isolating and measuring the substantial interactive effect of the acceleration of abiotic bank erosion facilitated by biotic activity. Biotic energy expended through burrowing represents an energy surcharge to the river system that can augment sediment erosion by geophysical mechanisms.

Impacts of Extreme Weather Events on Hydromorphology of UK Rivers

In this study, we assessed the effects of extreme weather events on Hydro-morphological Quality Elements in rivers of the United Kingdom alongside other pressures that will provide significant challenges for the implementation of the Water Framework Directive in the UK in terms of cost-effectiveness and sustainability. While observed meteorological data and river data sets were used for assessing changes in river systems and weather patterns, for future assessments, UK Climate Projections 2018 data was used. The studies in the literature have shown that during periods of extreme events, the river hydro-morphology is affected especially in terms of river flows, sediments and riparian zones such as draughts, and intense and heavy rainfall leading to reduced or exceptionally high flow respectively. Reduced flows can lead to the loss of habitat of aquatic organisms and an increase in fish deaths. Whilst increased river flows lead to changes of the hydro-morphology of rivers including changes to sediment dynamics and channels, rivers are also under negative effects of anthropogenic hydro-morphological pressures such as building dams and water abstractions. Furthermore, changes in river hydro-morphology can cause other problems such as increasing water temperature and decreasing dissolved oxygen, and thereby degrading Biological Quality Elements and Physico-Chemical Quality Elements. To deal with and mitigate these problems, a holistic view of water policy that considers climate change projections, reduces water demand, changes agricultural and urban land use practices, improves water availability and quality is required.

The Met Office Operational Soil Moisture Analysis System

In this study, the current Met Office operational land surface data assimilation system used to produce soil moisture analyses is presented. The main aim of including Land Surface Data Assimilation (LSDA) in both the global and regional systems is to improve forecasts of surface air temperature and humidity. Results from trials assimilating pseudo-observations of 1.5 m air temperature and specific humidity and satellite-derived soil wetness (ASCAT) observations are analysed. The pre-processing of all the observations is described, including the definition and construction of the pseudo-observations. The benefits of using both observations together to produce improved forecasts of surface air temperature and humidity are outlined both in the winter and summer seasons. The benefits of using active LSDA are quantified by the root mean squared error, which is computed using both surface observations and European Centre for Medium-Range Weather Forecasts (ECMWF) analyses as truth. For the global model trials, results are presented separately for the Northern (NH) and Southern (SH) hemispheres. When compared against ground-truth, LSDA in winter NH appears neutral, but in the SH it is the assimilation of ASCAT that contributes to approximately a 2% improvement in temperatures at lead times beyond 48 h. In NH summer, the ASCAT soil wetness observations degrade the forecasts against observations by about 1%, but including the screen level pseudo-observations provides a compensating benefit. In contrast, in the SH, the positive effect comes from including the ASCAT soil wetness observations, and when both observations types are assimilated there is a compensating effect. Finally, we demonstrate substantial improvements to hydrological prediction when using land surface data assimilation in the regional model. Using the Nash-Sutcliffe Efficiency (NSE) metric as an aggregated measure of river flow simulation skill relative to observations, we find that NSE was improved at 106 of 143 UK river gauge locations considered after LSDA was introduced. The number of gauge comparisons where NSE exceeded 0.5 is also increased from 17 to 28 with LSDA.

Thermal sensitivity of feeding and burrowing activity of an invasive crayfish in UK waters

AbstractClimate change and invasive species are among the biggest threats to global biodiversity and ecosystem function. Although the individual impacts of climate change and invasive species are commonly assessed, we know far less about how a changing climate may impact invading species. Increases in water temperature due to climate change are likely to alter the thermal regime of UK rivers, and this in turn may influence the performance of invasive species such as signal crayfish (Pacifastacus leniusculus), which are known to have deleterious impacts on native ecosystems. We evaluate the relationship between water temperature and two key performance traits in signal crayfish—feeding and burrowing rate—using thermal experiments on wild‐caught individuals in a laboratory environment. Although water temperature was found to have no significant influence on burrowing rate, it did have a strong effect on feeding rate. Using the thermal performance curve for feeding rate, we evaluate how the thermal suitability of three UK rivers for signal crayfish may change as a result of future warming. We find that warming rivers may increase the amount of time that signal crayfish can achieve high feeding rate levels. These results suggest that elevated river water temperatures as a result of climate change may promote higher signal crayfish performance in the future, further exacerbating the ecological impact of this invasive species.

The problem of underpowered rivers

AbstractThis study has hypothesized that for many rivers the trade‐off between flow accumulation and the decrease in slope along channel length means that stream power increases downstream and, moreover, that given the low slope angles in headwater and low‐order streams, they would have insufficient stream power to erode let alone transport sediment. The study considered the stream power profile, the particle travel distances and the application of the Hjulström curve based on the velocity profile of nine, large UK catchments. The study showed that: Some rivers never showed a maximum in their longitudinal stream power profile, implying that some rivers never develop a deposition zone before they discharge at the tidal limit. Particle travel distances during a bankfull discharge event showed that for some rivers 91% of the upper main channel would not be cleared of sediment. Furthermore, while some rivers could transport a 2 mm particle their entire length in one bankfull event, for another river it would take 89 such events. The Hjulström curve shows that for three of the study rivers the upper 20 km of the river was not capable of eroding a 2 μm particle. The study has shown that for all rivers studied, erosion is focused downstream and deposition upstream. Many UK rivers have a dead zone where, on time scales of the order of centuries, no erosion or transport occurs and erosion only occurs in the lower courses of the channel where discharge rather than slope dominates – we propose these as underpowered rivers. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Can aspects of the discharge regime associated with juvenile Atlantic salmon (Salmo salar L.) and trout (S. trutta L.) densities be identified using historical monitoring data from five UK rivers?

AbstractUnderstanding salmonid discharge requirements can help inform management to conserve wild populations in a changing climate. This study developed Bayesian hierarchical mixed‐effects models relating 0+ Atlantic salmon (Salmo salar L.) and trout (Salmo trutta L.) densities to different aspects of river discharge. Associations between these densities and nine hydrological variables representing the magnitude, frequency and duration of discharge events were evaluated using historical monitoring data from 36 sites on five rivers in England and Wales. All hydrological variables had weak associations with 0+ salmonid densities. More frequent high discharges between spawning and emergence were positively and negatively associated with 0+ salmon and trout densities, respectively. High discharges might increase spawning site availability for salmon and decrease egg‐to‐fry survival for trout. However, overall, only equivocal evidence was found regarding which discharge aspects affect juvenile salmonid densities. Therefore, a strategic review of juvenile salmonid monitoring programmes integrating environmental data collection is recommended.

Development and application of eDNA-based tools for the conservation of white-clawed crayfish

eDNA-based methods represent non-invasive and cost-effective approaches for species monitoring and their application as a conservation tool has rapidly increased within the last decade. Currently, they are primarily used to determine the presence/absence of invasive, endangered or commercially important species, but they also hold potential to contribute to an improved understanding of the ecological interactions that drive species distributions. However, this next step of eDNA-based applications requires a thorough method development. We developed an eDNA assay for the white-clawed crayfish (Austropotamobius pallipes), a flagship species of conservation in the UK and Western Europe. Multiple subsequent in-situ and ex-situ validation tests aimed at improving method performance allowed us to apply eDNA-based surveys to evaluate interactions between white-clawed crayfish, crayfish plague and invasive signal crayfish. The assay performed well in terms of specificity (no detection of non-target DNA) and sensitivity, which was higher compared to traditional methods (in this case torching). The eDNA-based quantification of species biomass was, however, less reliable. Comparison of eDNA sampling methods (precipitation vs. various filtration approaches) revealed that optimal sampling method differed across environments and might depend on inhibitor concentrations. Finally, we applied our methodology together with established assays for crayfish plague and the invasive signal crayfish, demonstrating their significant interactions in a UK river system. Our analysis highlights the importance of thorough methodological development of eDNA-based assays. Only a critical evaluation of methodological strengths and weaknesses will allow us to capitalise on the full potential of eDNA-based methods and use them as decision support tools in environmental monitoring and conservation practice.